This invention relates to the linearization of the gain and phase transfer characteristics of solid state power amplifiers and traveling wave tube amplifiers, wherein a preceding linearizer circuit is deployed by means of vectorial summation of signals of linear and nonlinear channels having diode circuits constructed by use of coplanar waveguide.
Predistortion linearizers are used in transmitter applications having simultaneous requirements of high efficiency and of low distortion, wherein the low distortion includes a conversion from an amplitude modulated signal to a distorted amplitude modulated signal as well as introduction of unwanted phase modulation from an amplitude modulated signal. These two requirements are generally mutually exclusive since high efficiency is achieved by operating a power amplifier near power saturation, whereas low distortion requires that the operating point be set back from the power-saturation region. Thus, if one were to plot the amplitude of the output signal of a high-gain microwave amplifier versus the input signal, the gain of the amplifier would appear to decrease with increasing input signal amplitude. In addition, the amount of phase shift which is present for a relatively small input signal amplitude would change as the amplifier gain tends to saturate for high input signal levels.
Therefore, there is a problem because existing amplifiers can be employed for linear amplification over only a relatively small range of input signal levels. Operation at saturation, while useful in attaining high values of efficiency suffers from the foregoing forms of signal distortion. A further problem arises in an attempt to build a gain linearization circuit operable at microwave frequencies in that parasitic resonances can occur as a result of the circuit implementation.